For Apache Hadoop applications to be able to interact with Amazon S3, they must know the
AWS access key and the secret key. This can be achieved in three different ways: through configuration properties, environment variables, or instance metadata. While the first two options can be
used when accessing S3 from a cluster running in your own data center. IAM roles, which use
instance metadata should be used to control access to AWS resources if your cluster is running
on EC2.